1. Field of the Invention
The present invention relates to a method of desensitizing a color developer to be used with a color former employing a desensitizer composition. More particularly, the present invention relates to a method of desensitizing using a desensitizer composition which reduces or extinguishes the function of the developer (solid electron accepting compound) for developing the color former (substantially colorless electron donor organic compound).
2. Description of the Prior Art
It is well known that a developed color image can be obtained by contacting a color former with a developer. This phenomenon is utilized in pressure sensitive copying papers (see U.S. Pat. Nos. 2,505,470, 2,505,489, 2,550,471, 2,548,366, 2,712,507, 2,730,456, 2,730,457, and 3,418,250, etc.), and heat sensitive recording papers (see Japanese Patent Publication No. 4160/1968 and U.S. Pat. No. 2,939,009, etc.), etc. Furthermore, a printing method in which a developed color image is obtained by supplying a color former containing ink through a screen such as a stencil to a developer coated sheet, is known (see German Patent Laid Open No. 1,939,962).
A pressure sensitive copying paper is produced by dissolving the color former in a solvent such as chlorinated paraffin, alkyl naphthalene, alkylated diphenylethane, and alkylated diphenylmethane; dispersing the resulting solution in a binder or microencapsulating the solution; and then coating the dispersion on a support such as paper and plastic film, etc.; and, on the other hand, coating an acid clay, a phenol-formaldehyde resin, metal salts of aromatic carboxylic acids, etc., as the developer. A heat sensitive recording paper is produced by coating the color former and developer together with a heat meltable material such as acetanilide on a support. In this case, the heat meltable material melts on heating and dissolves the color former.
In general, the color former and the developer are coated on the same side or opposite sides of the support or on different supports. Thus, it is necessary that the color forming reaction is prevented from occuring at portions where the formation of the developed color image is not needed or should be inhibited. For this purpose, a desensitizer has been conventionally partially coated on the developer coated layer, thereby preventing the color forming reaction.
As the desensitizer, high molecular weight primary alkylamines such as dodecyl amine, and quaternary ammonium salts such as dodecyl trimethyl ammonium chloride, as described in U.S. Pat. No. 2,777,780; tertiary amines prepared from ethylene oxide and a monoalkylamine, an aralkylamine, or an ethanolamine, as described in Japanese Patent Publication No. 29546/1971; secondary alkylamines, such as didodecylamine; tertiary amines, such as triethylamine; primary arylamines, such as aniline; and aralkylamines, such as benzylamine; etc. are known.
These desensitizers, however, have drawbacks and more excellent desensitizers with better properties have been desired. For instance, since a desensitizer having a high desensitizing effect is water-soluble and of very high hygroscopicity, when it is used as a desensitizing ink, the ink absorbs moisture, particularly at high humidity, thereby separating a binder and thus the viscosity of the ink is insufficient and coating of the ink cannot be carried out smoothly. Moreover, when the desensitizer is allowed to stand together with microcapsules, the water absorbed in the desensitizer swells the wall of the microcapsule and in some cases, breaks the wall. Unpleasant odor, coloring of the coated surface, the discoloration of printing with the color ink are also disadvantages of the prior art desensitizers.